I can not make changes to layout. For example, if I need larger project monitor, I can not do it. Layout stays fixed. This is only with this version. I’m now trying with my laptop Lenovo Yoga 2 Pro and don’t have now external monitor.
I used Shotcut 2 years ago a lot, but it was then too unstable for me, even I liked it a lot. Now I wanted to try it again, but the program did not function in proper way. May be it is because of my distro Ubuntu Gnome 18.04. Or what it could be?

Why can you not? What are you trying? It works fine for me. Maybe you are not trying hard enough to re-arrange the panels or access the divider between panels. Try some of the different options under View > Layout menu. Show us a screenshot.